Proof.--This proposition is
self-evident. He, who knows how to
distinguish between
true and
false,
must have an adequate idea of true and
false. That is (E2P40N2), he
must know the true and the false by the
second or
third kind of knowledge.

E2:
PROP. 43. He, who has a
true idea, simultaneously
knows that he has a
true idea,
and cannot doubt
of the truth of the thing perceived.

Proof.--A
true idea in us
is an idea which is
adequate in God, in so
far as he is displayed through the nature of the
human mind
(E2P11C).
Let us suppose that there is in God, in so far as he is displayed through
the human mind, an
adequate idea, A.
The idea of this idea must also
necessarily be in God, and be referred to him in the same way as the idea
A (by E2P20, whereof the proof is of
universal application). But the
idea A is supposed to be referred to God, in so far as he is displayed
through the human mind;
therefore, the idea of the idea A must be referred
to God in the same manner; that is
(by E2P11C), the
adequate idea of
the idea A will be in the mind, which has the adequate idea A; therefore
he, who has an
adequate idea
or knows a thing truly
(E2P34), must at the
same time have an
adequate idea
or true knowledge of his knowledge; that
is, obviously, he must be assured. Q.E.D.

E2: PROP. 43, Note.
--I explained in the note E2P21N what is
meant by the idea of an
idea; but we may remark that the foregoing proposition
E2P43 is in
itself sufficiently plain. No one, who has a
true idea, is ignorant that a
true idea involves the highest
certainty. For to have a
true idea is only
another expression for knowing a thing perfectly, or as well as possible.
No one, indeed, can
doubt of this,
unless he thinks that an idea is
something lifeless, like a picture on a panel, and not a
mode of thinking-
-namely, the very act of
understanding.
And who, I ask, can know that he
understands anything, unless he do first understand it? In other words,
who can know that he is sure of a thing, unless he be first sure of that
thing? Further, what can there be more clear, and more
certain, than a
true idea as a standard of truth? Even as light displays both itself and
darkness, so is truth a standard both of itself and of
falsity.
I think I
have thus sufficiently answered these questions--namely, if a
true idea is
distinguished from a
false idea,
only in so far as it is said to agree
with its object, a true idea has no more reality or perfection than a
false idea (since the two are only distinguished by an extrinsic mark);
consequently, neither will a man who has true ideas have any advantage
over him who has only false ideas. Further, how comes it that men have
false ideas? Lastly, how can anyone be sure, that he has ideas which
agree with their objects? These questions, I repeat, I have, in my
opinion, sufficiently answered. The difference between a
true idea and a
false idea
is plain: from what was said in E2P35,
the former is related
to the latter as being is to not-being. The causes of
falsity I have set
forth very clearly in E2P19 and [up to]
E2P35 with the note
E2P35N. From
what is there stated, the difference between a man who has
true ideas, and
a man who has only
false ideas, is made apparent.
As for the last
question--as to how a man can be sure that he has ideas that agree with
their objects, I have just pointed out, with abundant clearness, that his
knowledge arises from the simple fact, that he has an idea which
corresponds with its object--in other words, that truth is its own
standard. We may add that our
mind, in so far as it perceives things
truly, is part of the infiniteintellect of God
(E2P11C); therefore,
the clear and distinct ideas
of the mind
are as necessarily true as the ideas of God.

E2: PROP. 44 Corollary 1,
Note.
--How this way of looking at things arises, I will briefly explain. We
have shown above (E2P17 and Coroll.
E2P17C) that the
mind always
regards things as present to itself, even though they be not in existence,
until some causes arise which exclude their existence and presence.
Further (E2P18), we showed that, if
the human body has once been
affected by two external bodies simultaneously, the mind, when it
afterwards imagines one of the said external bodies, will straightway
remember the other--that is, it will regard both as present to itself,
unless there arise causes which exclude their existence and presence.
Further, no one doubts that we imagine
time, from the fact that we imagine
bodies to be moved some more slowly than others, some more quickly, some
at equal speed.
Thus, let us suppose that a
child yesterday saw Peter for
the first time in the morning, Paul at noon, and Simon in the evening;
then, that to-day he again sees Peter in the morning. It is evident, from
E2P18, that, as soon as he sees the
morning light, he will imagine that
the sun will traverse the same parts of the sky, as it did when he saw it
on the preceding day; in other words, he will imagine a complete day, and,
together with his
imagination
of the morning, he will imagine Peter; with
noon, he will imagine Paul; and with evening, he will imagine Simon--that
is, he will imagine the existence of Paul and Simon in relation to a
future time; on the other hand, if he sees Simon in the evening, he will
refer Peter and Paul to a
past time, by imagining them simultaneously with
the imagination
of a past time.
If it should at any time happen, that on
some other evening the child should see James instead of Simon, he will,
on the following morning, associate with his imagination of evening
sometimes Simon, sometimes James, not both together: for the child is
supposed to have seen, at evening, one or other of them, not both
together. His
imagination
will therefore waver; and, with the imagination
of future evenings, he will associate first one, then the other--that is,
he will imagine them in the future, neither of them as certain, but both
as contingent.
This wavering of the imagination
will be the same, if the
imagination
be concerned with things which we thus contemplate, standing
in relation to time past or time present: consequently, we may imagine
things as contingent,
whether they be referred to
time present, past, or future.

E2:
PROP. 44, Corollary 2.--It is in the nature of
reason to perceive things under a
certain form of eternity (sub quadam aeternitatis specie).

Proof.--It is in the nature
of reason to regard things, not as
contingent,
but as necessary (E2P44).
Reason
perceives this necessity of
things (E2P41) truly--that is
(E1A6), as it is in itself. But
(E1P16) this necessity of things is
the very necessity of the
eternal
nature of God; therefore, it is in the nature of
reason to regard things
under this form of eternity. We may add that the bases of
reason are the
notions (E2P38), which answer to
things common to all, and which
(E2P37) do not answer to the
essence
of any particular thing:
which must therefore be conceived without any relation to time,
under a certain form of eternity.

Proof.--The proof of the last
proposition is universal; and whether a
thing be considered as a part or a whole, the idea thereof, whether of the
whole or of a part (by the last Prop.
E2P45), will involve
God'seternal
and infiniteessence.
Wherefore, that, which gives knowledge of the
eternal and
infinite
essence of God,
is common to all, and is equally in the part and in the whole; therefore
(E2P38) this knowledge will be
adequate. Q.E.D.

E2: PROP. 47, Note.
--Hence we see, that the
infiniteessence and the eternity of
God are
known to all. Now as all things are in God, and are conceived through God,
we can from this knowledge infer many things, which we may
adequately
know, and we may form that
third kind of knowledge
of which we spoke in
the note E2P40N2, and of the excellence and
use of which we shall have
occasion to speak in Part 5 (E5).
Men have not so clear a knowledge of
God as
they have of general notions, because they are unable to imagine God as
they do bodies, and also because they have associated the name God with
images
of things that they are in the habit of seeing, as indeed they can
hardly avoid doing, being, as they are, men, and continually affected by
external bodies.
Many errors, in truth, can be traced to this head,
namely, that we do not apply names to things rightly. For instance, when a
man says that the lines drawn from the centre of a circle to its
circumference are not equal, he then, at all events, assuredly attaches a
meaning to the word circle different from that assigned by mathematicians.
So again, when men make mistakes in calculation, they have one set of
figures in their mind, and another on the paper. If we could see into
their minds, they do not make a mistake; they seem to do so, because we
think, that they have the same numbers in their mind as they have on the
paper. If this were not so, we should not believe them to be in error, any
more than I thought that a man was in error, whom I lately heard
exclaiming that his entrance hall had flown into a neighbour's hen, for
his meaning seemed to me sufficiently clear.
Very many controversies have
arisen from the fact, that men do not rightly explain their meaning, or do
not rightly interpret the meaning of others. For, as a matter of fact, as
they flatly contradict themselves, they assume now one side, now another,
of the argument, so as to oppose the opinions, which they consider
mistaken and absurd in their opponents.